The Indonesian National Disaster Mitigation Agency (BNPB) has issued an alert warning regarding Mount Sinabung in Karo regency, North Sumatra, after finding increased volcanic activity. At the same time, some residents living near the massive Toba supervolcano are reporting heat, hot steam and gas emanating from the ground.

BNPB spokesperson Sutopo Purwo Nugroho said that Sinabung has the potential to spread hot ash clouds to the south and southeast as far as 7km, and the volume of lava coming from the mountain has reached 3 million cubic meters. A call for residents within 7km of the crater to evacuate has also been made. Mount Sinabung has seen two previous eruptions in recent years, once in 2010, and again in 2013.

Mount Sinabung is 25km from the Toba supervolcano, who’s last eruption, estimated to have occurred 69,000 to 77,000 years ago, is believed to have been the cause of the genetic bottleneck in humans of that time, as shown in a recent mitochondrial DNA study. An increase of seismic activity in the region of this supervolcano, like that of Mount Sinabung, raises concerns over the potential for resumed volcanic activity in Lake Toba.

Rovicky Dwi Putrohari, President of the Indonesia Geological Experts Association, commented on Lake Toba in 2013: "A quake could reactivate the magma chamber which is so far dormant. That’s why we believe Mount Toba could erupt again at any time. When it will be, we don’t know. Thorough and continuous research is needed to find that out."